SEER is an authoritative source of information on cancer incidence and survival in the United States. SEER currently collects and publishes cancer incidence and survival data from population-based cancer registries covering approximately 28 percent of the U.S. population.

SEER Inquiry System - View

Question
MP/H Rules/Multiple primaries--Breast: Is the diagnosis of Paget disease two years after a diagnosis of infiltrating duct carcinoma of the same breast a new primary? See discussion.

Discussion
A patient was diagnosed and treated in 2010 for infiltrating duct carcinoma of the left breast. There was no mention of Paget disease. Then in 2012, the same patient was diagnosed with Paget disease of the nipple of the left breast. Rule M9 seems to apply; so this is the same primary, correct? And the information about the Paget disease is simply never captured, correct?

Answer
Yes, Rule M9 makes this a single primary. You could revise the original histology code to 8541/3 on the assumption that Paget was present at the original diagnosis, but not yet identified.